As a back frame of a vehicle seat, there is one which is attached to a lower arm member, which is attached to a cushion frame, via a recliner so that an inclination angle to the cushion frame can be adjusted. In such a type of a back frame disclosed in JP-A-2011-132917, the back frame is connected, via a recliner, to a rear portion of a lower arm member that is integrated with side frames, which are plate-like members, disposed opposite to each other with a space therebetween on the left and right sides of the cushion frame. An energy absorption part configured by a concave portion formed by recessing part of the plate-like member is formed on the lower member. When a large bending load is applied to the back frame due to rear collision or the like of a vehicle, the energy absorption part is deformed to absorb the energy generated by the rear collision or the like.
In the above-described structure, the lower arm member is a single plate-like member, and an energy absorption part configured by a concave portion is formed on a part of the lower arm member. In this way, when a large bending load is applied to the back frame due to rear collision or the like of a vehicle, there is a possibility that the lower arm member is deformed and falls down not only in an upper and lower direction but also in a seat width direction. When the lower arm member is deformed so as to fall down in the seat width direction, the back frame also moves so as to fail down in the seat width direction, and the supporting performance for a seated occupant is deteriorated. Therefore, in order to deform the lower arm member in the upper and lower direction in a well-balanced manner at the time of fear collision of a vehicle, trial and errors are required to optimize the structure of the lower arm member and the shape of the energy absorption part or the like.
The disclosure aims to provide a back frame attachment structure of a vehicle seat, which is capable of absorbing energy at the time of rear collision or the like of a vehicle by suppressing, deformation in the seat width direction. of the lower arm member with a simple structure, and a vehicle seat.
According to an aspect of the disclosure, there is provided a back frame attachment structure of attaching a hack frame of a vehicle seat to a vehicle body side member, wherein the back frame includes a pair of side frames extending in an upper and lower direction with a space in a seat width direction, wherein a lower end portion side of at least one of the pair of side frames is attached to an upper portion of a lower arm member whose lower portion is fixed to the vehicle body side member, wherein the lower arm member includes two plate-like members which are superimposed with each other in the seat width direction, the upper portion of the lower arm member and the lower portion of the lower arm member being connected to each other by a front connection portion located on a front side and a rear connection portion located on a rear side, and the front connection portion and the rear connection portion being separated by a through-hole located at a middle of the lower arm member when viewed from the seat width direction, and wherein, when a large load due to collision or the like of a vehicle is applied to the back frame, the two plate-like members are configured to absorb energy by being deformed to be separated from each other in the seat width direction by a compressive load in the upper and lower direction generated in the front connection portion or the rear connection portion.
Accordingly, when large load due to collision or the like of the vehicle is applied to the back frame, a strong compressive load in the upper and lower direction is generated in tire rear connection portion at the time of rear collision and is generated in the front connection portion at the time of front collision. At this time, since the rear connection portion and front connection portion are formed by superimposing the two plate-like members in the seat width direction, the two plate-like members are respectively buckled so as to be separated from each other in the seat width direction, thereby absorbing energy. In this way, the rear connection portion and the front connection portion are easily deformable in the upper and lower direction and are difficult to fall down in the seat width direction, so that the deformation in the left and right direction of the lower arm member can be suppressed by a simple structure in either case of front collision or rear collision.
According to another aspect of the disclosure, there is provided a vehicle seat including: a back frame including a pair of side frames extending in an upper and lower direction with a space in a seat width direction; a lower arm member including two plate-like members which are superimposed with each other in the seat width direction, an upper portion of the lower Linn member being connected to at least one of the pair of side frames; and a cushion frame to which a lower portion of the lower arm member is fixed, wherein the upper portion of the lower arm member and the lower portion of the lower arm member are connected to each other by a front connection portion located on a front side and a rear connection portion located on a rear side, the front connection portion and the rear connection portion being separated by a through-hole located therebetween, and wherein at least one of the front connection portion and the rear connection portion includes a deformation promoting portion configured to promote deformation of the two plate-like members in a direction separated from each other.